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What is Aerobic Respiration? – Definition, Diagram, Process

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  • Last Updated : 23 Jul, 2022
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Inside living cells, a metabolic biochemical mechanism known as respiration is responsible for the conversion of complicated dietary material into a form that may be used to produce energy molecules known as ATP. It is a chain of oxidation-reduction processes that, in the end, result in the release of energy in the form of the molecule known as adenosine triphosphate (ATP), which is then preserved. During the course of this process, an electron moves from a donor to an acceptor. In the broadest sense, respiration may be seen as the process of taking in oxygen and giving out carbon dioxide gas. However, this process is referred to as breathing rather than respiration.

Do Plants Need Oxygen to Live?

There is some truth to the common misconception that plants do not breathe. To be able to respire, plants need oxygen, but this process also results in the release of carbon dioxide. Stomata, which are located in the leaves, and lenticels, which are found in the stems, are both actively engaged in the process of gaseous exchange in plants. However, unlike people and animals, plants do not contain any specific structures for the exchange of gases. When compared to human beings and animals, the rate of respiration in plant leaves, stems, and roots is much slower. The act of breathing is distinct from the process of respiration. The process of respiration includes the phase of breathing, which occurs in both animals and humans. Plants breathe in a way that is distinct from animal breathing via a process that is known as cellular respiration. Plant cells need the energy to exist, hence plants must engage in respiration throughout their whole lives.

Plants manufacture glucose molecules via the process of photosynthesis, which is part of the process of cellular respiration. This process involves absorbing energy from sunlight and transforming it into glucose. Numerous experiments conducted in real-time shed light on the process by which plants consume oxygen and expel carbon dioxide. The process of respiration is essential for all plant life because it provides the cells with the necessary fuel to function. The cycle of respiration that takes place in plants When respiration occurs in various plant sections, the amount of gas exchanged is greatly reduced. As a result, every component receives the nourishment and power it needs to function properly. As a direct consequence of this, the leaves, stems, and roots of plants each conduct their own unique gas exchange. Stomata are tiny pores that are found in leaves and enable again for replacement of oxygen and carbon dioxide. The oxygen that is taken in by the plant via its stomata is utilized by the cells of the leaf to facilitate the breakdown of glucose into water and carbon dioxide.

Different Methods of Breathing(or)Respiration

There are two primary methods of breathing in and out: Aerobic respiration and Anaerobic respiration

Aerobic Respiration

Aerobic Respiration


Where exactly is the process of aerobic respiration carried out?

Within the mitochondria of animal cells, three out of the four phases of the aerobic respiration process are carried out. The process of glycolysis takes place in the cytoplasm, which is the fluid that surrounds the organelles inside the cell Within the mitochondria, three distinct chemical events take place: the link reaction, the TCA, or Krebs(tricarboxylic acid cycle), and oxidative phosphorylation. The process of cellular respiration known as aerobic respiration takes place when oxygen is present. 

Cellular respiration

During the respiratory process, one electron is moved from mono oxygen molecules (O1) to dioxygen molecules (O2), which results in the production of water molecules and the energy molecule ATP. At this point, the glucose molecule is entirely oxidized, resulting in the production of water, carbon dioxide, and energy (ATP).

The chemical equation for the aerobic respiration process reads as follows:

C6H12O6 (glucose) + O2 (oxygen)  converts to 6CO2 (carbon dioxide) + 6H2O (water) + ATP (Energy)

In order to make 32 molecules of ATP, one molecule of glucose must first be oxidized, which results in the production of 6 molecules of CO2,  and 6 molecules of water(H2O), and so on. In the aerobic and facultative modes of respiration, it can be found in the vast majority of living creatures, including all higher plants and animals as well as the majority of microbes. It is found in the cytoplasm of cells belonging to prokaryotes and the mitochondria of cells belonging to eukaryotes. In comparison to the anaerobic kind, this one moves at a more leisurely pace yet produces more molecules of ATP. It is possible to manufacture a total of 32 unique molecules of ATP from a single glucose molecule. Glucose, amino acids, and fatty acids are metabolized in the presence of oxygen during this process. The starting material for this method is glucose.

Steps Involved in aerobic cellular respiration

This complex multistep enzymatic reaction process may be broken down into four stages:

  • Glycolysis(glucose splitting)
  • Oxidation of pyruvic acid
  • The Krebs cycle(or)TCA cycle and
  • Oxidative phosphorylation.

Each stage is already a complicated enzymatic chemical reaction process that takes place in several steps.

Glycolysis(or)Glucose splitting

Etymology: The name “glycolysis” originates from the Greek words “glycose,” which means “sugar,” and “lysis,” which means “dissolution.”

The process of glycolysis involves a series of catabolic events that, with the help of various enzymes, turn glucose (or glycogen) molecules into pyruvic acid. During the process, one molecule of glucose functions as a catalyst. This leads to the creation of 2  molecules each of pyruvic acid, nicotinamide adenine dinucleotide, and adenosine triphosphate. It is also sometimes referred to as the “EMP Pathway” or the “Embden-Meyerhof-Parnas Pathway.” Glucose plus two molecules of NAD+ plus two molecules of ADP plus two molecules of pi results in two molecules of pyruvate plus two molecules of NADH plus two molecules of ATP plus two molecules of hydrogen ions. Within the cytosol of almost every cell that makes up the human body, it is possible to find it. It may take place in either an aerobic or anaerobic environment. Pyruvic acid is created when aerobic circumstances are present, while lactic acid is produced when anaerobic ones are present.

The glycolysis process is the first phase in the aerobic respiration process. During this step, glucose is broken down into simpler sugars. It is a reaction process that takes place in many steps. The course of the reaction may be divided into three distinct stages, which are as follows:

Initial Investing in Energy Phase (Preparatory Phase)

In a three-step process, the first phase is termed the energy investment phase because it involves the conversion of glucose to fructose-1, 6-bisphosphate utilizing two molecules of ATP. This phase is also known as the glycolysis phase.

  • The phosphate-dependent glycolysis of glucose In this stage, the enzyme is known as “hexokinase” and 1 molecule of ATP is required. During this step, glucose is converted into glucose-6-phosphate.
  • Isomerization of glucose – 6 – phosphate (G-6-P): In this step, the enzyme is known as glucose – 6 – phosphate isomerase is responsible for catalyzing the reversible isomerization of G-6-P to fructose – 6 – phosphate in the presence of Mg+2 ion.
  • Phosphorylation of fructose-6-phosphate (F-6-P): In this step, F-6-P is phosphorylated by the “phosphofructokinase” enzyme, which results in the production of fructose-1,6-bisphosphate. This stage of glycolysis is referred to as the committed step.

The Phase of Splitting

It is a two-step process in which the molecule of 6-carbon fructose-1,6-bisphosphate is divided into two 3-carbon molecules called glyceraldehyde-3-phosphate.

  • The fragmentation of fructose – 1,6 – bisphosphate: It is changed into 2 triose phosphate; glyceraldehyde – 3 – phosphate (G – 3 – P) and DHAP(Dihydroxyacetonephosphate), by an enzyme called “aldolase.” 
  • The formation of fructose – 1,6 – phosphate: Fructo (fructose bisphosphate aldolase).
  • Isomerization of triosephosphate: The enzyme known as “triosephosphate isomerase” is responsible for the reversible conversion of dihydroxyacetone phosphate to Glyceraldehyde-3-Phosphate.

The Phase of Energy Generation

During this last step of the process, the molecules of glyceraldehyde-3-phosphate are transformed to pyruvate. The following chain of chemical reactions is included in it:

  • Oxidation of glyceraldehyde – 3 – phosphate (G-3-P): The enzyme is known as “glyceraldehyde – 3 – phosphate dehydrogenase” and converts G – 3 – P into 1,3 – bisphosphoglycerate while simultaneously creating a molecule of NADH.
  • The transfer of phosphoryl groups from 1,3-bisphosphate to adenosine diphosphate (ADP): the enzyme known as “phosphoglycerate kinase” is responsible for the reversible conversion of 1,3-bisphosphate to 3-phosphoglycerate. During this procedure, a molecule of ATP is created from scratch.
  • The conversion of 3 – phosphoglycerate to 2 – phosphoglycerate is catalysed by the enzyme known as “phosphoglycerate mutase.” This process takes place in step three.
  • Dehydration of 2-phosphoglycerate: The enzyme known as “enolase” is responsible for the dehydration of 2-phosphoglycerate, which results in the formation of phosphoenolpyruvate in a process that may be reversed.
  • Formation of Pyruvate: The last step in the formation of pyruvate is the transfer of the phosphoryl group from phosphoenolpyruvate to ADP, which results in the formation of a pyruvate molecule. Pyruvate kinase is the enzyme responsible for catalyzing this reaction.

Formation of Acetyl coenzyme-A

Pyruvate is changed into acetyl-coenzyme A, which is a prerequisite for entering the Krebs cycle, during the second phase of the process. Following this process, the pyruvate that was generated by glycolysis is subjected to oxidative decarboxylation. The enzyme is known as “pyruvate translocase” is responsible for the first step of transferring the pyruvate to the mitochondrial matrix. In an irreversible fashion, the transformation of pyruvic acid to acetyl-coenzyme A( acetyl-CoA) is carried out by an enzyme that is described as a “pyruvate dehydrogenase complex.” Pyruvate goes through the process of losing one of its carbon molecules, which ultimately leads to the production of a molecule of atmospheric co2 (CO2).In addition, NADH is produced from the reduction of NAD+ throughout the process.
One way to characterize the entire response is as follows: Pyruvate, when combined with NAD+ and CoA, may be converted into acetyl-CoA, which then produces carbon dioxide, NADH, and hydrogen ions.

Krebs Cycle

The end product of the glycolysis stage leads to the production of citric acid(or) tricarboxylic acid. Because of this, it is often referred to as the “Tricarboxylic Acid Cycle (TCA Cycle),” as well as the “Citric Acid Cycle.”
It is a cycle of oxidative reactions that take place in several phases, including the following steps:

  • The Formation of Citrate: The enzyme known as “citrate synthase” is responsible for the condensation of acetyl-CoA and oxaloacetate, which ultimately results in the creation of citric acid.
  • Isomerization of Citrate: The enzyme known as “aconitase” is responsible for isomerizing citrate into isocitrate, also known as isocitric acid. This occurs through an intermediary phase that results in the formation of cis-aconitate, which then rehydrates to produce isocitrate.
  • The formation of – ketoglutarate occurs when an enzyme known as “isocitrate dehydrogenase” converts isocitrate to oxalosuccinate first, and then decarboxylates the product to produce – ketoglutarate. During the reaction, a molecule consisting of CO2 and NADH is produced.
  • The Conversion of – Ketoglutarate to Succinyl CoA: The oxidative decarboxylation of – Ketoglutarate by the enzyme – Ketoglutarate Dehydrogenase leads to the synthesis of Succinyl CoA as well as CO2. NADH is created as a byproduct whenever NAD+ is employed in a process that requires an electron acceptor.
  • The Generation of Succinate “succinate thiokinase” is the enzyme responsible for the conversion of succinyl CoA into succinate. The enzyme nucleoside diphosphate kinase catalyses the phosphorylation of a molecule of GDP, which then results in the formation of a molecule of GTP.
  • Oxidation of Succinate: “Succinate dehydrogenase” oxidise succinic acid (succinate) to fumarate (fumaric acid). In the course of the process, a molecule of FADH2 is generated.
  • Hydration of Fumarate “Fumarase” catalyzes the conversion of fumarate to malate during the hydration of fumarate (malic acid). Malate is oxidised to oxaloacetic acid by the enzyme known as “malate dehydrogenase” in step number eight of the malate oxidation process (oxaloacetate). During this step, the NADH production process reaches its third and final stage. 

This is the last stage of the aerobic respiration process in the cell.

Phosphorylation via Oxidative Reduction

In this sequence of biological events, which are mediated by various enzymes, electrons are transferred from electron carriers such as NADH and FADH to an oxygen molecule (O2), resulting in the release of ATP molecules. This process is known as oxidative phosphorylation.

Total ATP molecules production details during respiration

ATP is used up during glycolysis, which results in the production of 2 ATP.

  • ATP created equals ATP generated four times over.
  • NADH generated equals two NADH, which equals two times 2.5, which equals five ATPs.
  • During the oxidative decarboxylation of pyruvate, NADH is created, which equals two NADH, which equals two times 2.5, which equals five ATPs.
  • Throughout the TCA Krebs Cycle
  • Because one molecule of glucose may result in the formation of two acetyl CoA molecules, the amount of ATP that can be generated by one cycle of the TCA pathway is increased by a factor of two.
  • Total NADH created equals 2 times 3 NADH, which equals 6 times 2.5, which equals 15 ATPs.
  • Total FADH2 generated equals two times one FADH2, which equals two times 1.5, which equals three ATPs.
  • Two ATPs are created in total via direct production.

During the process of oxidative phosphorylation, NADH and FADH2 are transformed into ATP, which may be found in the preceding section.

Total ATP YIELD = 7 (from glycolysis), 5 (from oxidative decarboxylation), and 20 (from TCA), which equals 32 ATPs

Frequently Asked Questions

Question 1: What is the main component required for the process of aerobic cellular respiration?


The gas (or) component required for the aerobic process is oxygen.

Question 2: What are the several steps of the process known as aerobic respiration?


  • Glycolysis(or)Glucose splitting to pyruvic acid
  • Acetyl coenzyme A generation
  • Kreb’s cycle (or)Tricarboxylic acid cycle
  • ETC (or) Electrons Transport chain.

Question 3: What are the products that are created at the conclusion of the aerobic respiration process?


In addition to the generation of 6 molecules of atmospheric CO2 and 6 molecules of water, the action of aerobic metabolism results in the synthesis of thirty molecules of the energy component called ATP.

Question 4: Why is it so important for organisms to engage in aerobic respiration?


The living creatures get the energy necessary to carry out all of the necessary activities of life via a process called aerobic respiration. Because of this, aerobic respiration is very significant.

Question 5: What are the many categories of aerobes, and what do they do?


The following are the several categories of aerobes: 

  • Obligate aerobes are required to have oxygen in order to thrive.
  • It is possible for facultative aerobes to flourish either in the presence of or in the absence of oxygen.
  • Microaerophiles are organisms that thrive in the presence of oxygen but are killed off by the high levels of oxygen found in the atmosphere.

Question 6: What is the ultimate byproduct of the glycolysis process?


Pyruvic acid is the end product of the process known as glycolysis.

Question 7:How many molecules of ATP are created while glycolysis is carried out?


During the process of glycolysis, 32 molecules of ATP are generated. 

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